Two siblings need to divide the family's responsibilities for caring for a sick relative. One of them says: I should get the lighter tasks because I live farther away. The other says: I should get the lighter tasks because I have younger children. Neither will budge. Both feel entitled. This is the problem that the fourth principle of principled negotiation addresses: when interests conflict and options are exhausted, how do you decide what is fair without either side simply giving in? The authors' answer is: insist on objective criteria. Objective criteria are standards that neither side invented for this negotiation — market value, precedent, expert opinion, legal standards, tradition, or independently determined benchmarks. They are external to both parties. Because they are not produced by either side, they are far harder to reject without looking unreasonable. When a buyer and seller of a house disagree on price, an independent property valuation is an objective criterion. When two business partners disagree on the value of a share, the last publicly traded price is an objective criterion. When siblings disagree on how to divide caregiving, time spent per week, distance travelled, and number of dependants are all objective criteria that both sides could apply. The authors explain why this matters. Positional bargaining asks: who has the stronger will? Objective criteria ask: what is fair, independent of either side's will? The first question leads to stubbornness and resentment. The second leads to conversation. Funmi is negotiating her salary for a new job in Abuja. The employer offers a figure that feels low. Instead of saying: I want more, or I need more, she says: according to industry data from similar roles in Abuja, the median salary for this position is X. Can you help me understand where this offer sits relative to that benchmark? She has introduced an objective criterion. Now the conversation is not about what she wants or what they want to pay. It is about what is defensible given the external reality of the market. That is a much easier conversation to have — and a much harder one for the employer to avoid. When using objective criteria, the authors advise: frame every issue as a joint search for a fair standard. Not: I deserve more. But: how should we decide what is fair here? Then propose specific criteria and be open to theirs.